(1) Field of the Invention
The present invention relates to a synchronization method and apparatus in redundant time-division-multiple-access (TDMA) communication equipment used for satellite communication and the like.
(2) Description of the Prior Art
Satellite communication networks and the like make use of the TDMA system. The TDMA system enables TDMA using a single radio frequency, but necessitates synchronization of transmission timing between stations.
A redundant transmission (TX) synchronization circuit used in TDMA communication equipment includes an active TX synchronization circuit and a standby TX synchronization circuit of the same construction. If the active circuit fails, the standby circuit takes over the operation. In the prior art, the synchronization between an active TX frame timing signal and a standby TX frame timing signal is frequently checked and corrected. Therefore, there is no problem in switching from the active circuit to the standby circuit when the failure occurs anywhere except in the TX synchronization circuits. If, however, an active TX frame counter fails and the timing of the active TX frame timing signal becomes abnormal, the timing of the standby TX frame timing signal will also become abnormal, thus making the existence of the redundant circuits meaningless.
Publications of interest in regard to the above-mentioned prior art are Japanese Unexamined Patent Publications (Kokai) Nos. 55-82550 and 56-89148.